Reactions of N,C,N-chelated pnictinidenes with Rh(I) and Ir(I) complexes: Coordination vs. Transmetalation

Combining geometric constraint and redox non-innocence within an ambiphilic PBiP pincer ligand

The synthesis of the first pincer ligand featuring a strictly T-shaped group 15 element and its coordination behaviour towards transition metals is described. The platform is itself derived from a trianionic redox non-innocent NNN scaffold. In addition to providing a rigid coordination environment to constrain a Bi centre in a T-shaped geometry to manipulate its frontier molecular orbital constitution, the NNN chelate displays highly covalent bonding towards the geometrically constrained Bi centre. The formation of intriguing ambiphilic Bi-M bonding interactions is demonstrated upon formation of a pincer complex as well as a multimetallic cluster. All compounds are comprehensively characterised by spectroscopic methods including X-ray Absorption Near Edge Structure (XANES) spectroscopy and complemented by DFT calculations.

Group 15 and 16 Nitrene-Like Pnictinidenes

Pnictinidenes are an increasingly relevant species in main group chemistry and generally exhibit proclivity for the triplet electronic ground state. However, the elusive singlet electronic states are often desired for chemical applications. We predict the singlet-triplet energy differences (ΔE_ST =E_Singlet -E_Triplet ) of simple group 15 and 16 substituted pnictinidenes (Pn-R; Pn=P, As, Sb, or Bi) with highly reliable focal-point analyses targeting the CCSDTQ/CBS level of theory. The only cases we predict to have favorable singlet states are P-PH₂ (-3.2 kcal mol^-1 ) and P-NH₂ (-0.2 kcal mol^-1 ). ΔE_ST trends are discussed in light of the geometric predictions as well as qualitative natural bond order analysis to elucidate some of the important electronic structure features. Our work provides a rigorous benchmark for the ΔE_ST of fundamental Pn-R moieties and provides a firm foundation for the continued study of heavier pnictinidenes.

(N),C,N-Coordinated Heavier Group 13-15 Compounds: Synthesis, Structure and Applications

The aim of this review is to summarize recent achievements in the field of (N),C,N-coordinated group 13-15 compounds not only regarding their synthesis and structure, but mainly focusing on their potential applications. Relevant compounds contain various types of N-coordinating ligands built up on an ortho-(di)substituted phenyl platform. Thus, group 13 and 14 derivatives were used as single-source precursors for the deposition of semiconducting thin films, as building blocks for the preparation of high-molecular polymers with remarkable optical and chemical properties or as compounds with interesting reactivity in hydrometallation processes. Group 15 derivatives function as catalysts in the Mannich reaction, in the allylation of aldehydes or activation of CO₂ . They were used as transmetallation reagents in transition metal catalysed coupling reactions. The univalent species serve as ligands for transition metals, activate alkynes or alkenes and are utilized as catalysts in the transfer hydrogenation of azo-compounds.

Recent developments in the chemistry of non-trigonal pnictogen pincer compounds: from bonding to catalysis

The combination of well-established meridionally coordinating, tridentate pincer ligands with group 15 elements affords geometrically constrained non-trigonal pnictogen pincer compounds. These species show remarkable activity in challenging element-hydrogen bond scission reactions, such as the activation of ammonia. The electronic structures of these compounds and the implications they have on their electrochemical properties and transition metal coordination are described. Furthermore, stoichiometric and catalytic bond forming reactions involving B-H, N-H and O-H bonds as well as carbon nucleophiles are presented.

Antimony(i) → Pd(ii) complexes with the (μ-Sb)Pd2 coordination framework

The reaction of the antimony(i) compound ArSb (1) (where Ar = C₆H₃-2,6-(CH[double bond, length as m-dash]NtBu)₂) with various dimeric allyl palladium(ii) complexes [Pd(η³-allyl)(μ-X)]₂ (where allyl = C₃H₅ or C₃H₄Me; X = Cl or CF₃CO₂) in a 1 : 1 stoichiometric ratio gave unique complexes with the μ-ArSb moiety bridging two palladium fragments, i.e. [{Pd(η³-C₃H₅)Cl}₂(μ-ArSb)] (2), [{Pd(η³-C₃H₄Me)Cl}₂(μ-ArSb)] (3) and [{Pd(η³-C₃H₅)(CF₃CO₂)}₂(μ-ArSb)] (4). Compound 1 serves formally as a 4e donor in 2-4. The treatment of 2 with another equivalent of ArSb led to the formation of the [Pd(η³-C₃H₅)(Cl)(μ-ArSb)] complex (5), proving that 1 is able to function as a 2e donor in target complexes as well. The structures of 2-5 were described in detail both in solution (NMR and mass spectrometry) and in the solid state (single crystal X-ray diffraction analysis). DFT methods were used to compare bonding in the 1 : 1 (5) and 1 : 2 (2) complexes. Furthermore, a comprehensive ¹²¹Sb Mössbauer spectroscopic investigation of complexes 2 and 5 along with parent ArSbCl₂ (6) and 1 was performed. For comparison, complexes [Fe(CO)₄(ArSb)] (7) and [Mo(CO)₅(ArSb)] (8) were also included in this study.

Heavier pnictinidene gold(i) complexes

N,C,N-Chelated pnictinidenes ArE [where E = As, Sb or Bi; Ar = 2,6-(tBuN[double bond, length as m-dash]CH)2C6H3] were used as ligands for the coordination of various gold(i) complexes. Thus, the reaction of ArE with [AuCl(Me2S)] gave complexes [AuCl(ArE)] [where E = As (1) or Sb (2)] that exhibited only limited stability in solution. By contrast, the reaction of ArBi with [AuCl(Me2S)] led to the immediate deposition of gold metal and the oxidation of the bismuth atom giving ArBiCl2. The treatment of a tetrameric gold alkynyl complex [Au(C[triple bond, length as m-dash]CPh)]4 with ArAs and ArSb gave ionic compounds [Au(ArAs)2]+[Au2(C[triple bond, length as m-dash]CPh)3]- [denoted as 3+[Au2(C[triple bond, length as m-dash]CPh)3]-] and [Au(ArSb)2]+[Au(C[triple bond, length as m-dash]CPh)2]- [denoted as 4+[Au(C[triple bond, length as m-dash]CPh)2]-], respectively. Finally, the reaction of ArE with the carbene gold(i) complex [Au(IPr)(MeCN)]+[BF4]- [where IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene, MeCN = acetonitrile] produced ionic complexes [Au(IPr)(ArE)]+[BF4]- [for cations: E = As (5+), Sb (6+) or Bi (7+)]. All complexes were characterized using 1H and 13C NMR, high mass accuracy electrospray ionization mass spectrometry (ESI-MS), IR and Raman spectroscopy and (except for 1) by single-crystal X-ray diffraction analysis. Furthermore, the structure and bonding of both neutral and ionic complexes with different coordination patterns have also been investigated in detail using a Density Functional Theory (DFT) computational approach.

Synthesis and non-conventional structure of square-planar Pd(ii) and Pt(ii) complexes with an N,C,N-chelated stibinidene ligand

The N,C,N-chelated stibinidene, ArSb (Ar = C6H3-2,6-(CH[double bond, length as m-dash]NtBu)2), reacts with Pt(ii) compounds [PtCl2L2] resulting in the formation of 1 : 1 complexes, cis-[PtCl2L(ArSb)] (L = Me2S (1), dmso (2)). In contrast, attempts to synthesize similar Pd(ii) complexes failed, resulting only in the formation of elemental palladium. To increase the stability of the ArSb complexes, in particular those containing Pd(ii), the simple auxiliary ligands were replaced with C,N-chelating ones, which led to a set of four compounds of the type [RMCl(ArSb)], where R = C6H4-2-(CH2NMe2) or Fe(η5-C5H4)(η5-C5H3-2-(CH2NMe2)) and M = Pd (3, 5) or Pt (4, 6). Compounds 1-6 were characterized by 1H and 13C{1H} NMR spectroscopy and single-crystal X-ray diffraction analysis, and in the case of ferrocene derivatives 5 and 6, also by cyclic voltammetry. Compounds 2-6 were shown to form rotamers in solution due to the side-on coordination of the ArSb ligand and a hindered rotation around the Sb-Pd(Pt) bond. This process was investigated by 1H-VT-NMR spectroscopy and by DFT computations.